1. Field of the Invention
The present invention relates to improvements of an ultrasonic Doppler diagnosis apparatus.
2. Description of the Related Art
There has been known an ultrasonic Doppler diagnosis apparatus based on the combination of an ultrasonic Doppler method and an ultrasonic pulse reflecting method. In the apparatus, information on blood stream and information on tomogram (B-mode image) are collected by a single ultrasonic probe, and are concurrently displayed in a real time manner. The principles to measure a blood velocity by the diagnosis apparatus of this type will be described below.
When an ultrasonic beam is projected onto a blood stream flowing through a human body as an object to be diagnosed, the ultrasonic beam is scattered by blood corpuscles and its center frequency "fc" is Doppler shifted by a frequency "fd". Accordingly, a receiving frequency "f" is the sum of the frequencies "fc" and "fd"; f=fc+fd. Those frequencies are mathematically expressed by EQU fd=(2V cos .theta./C).times.fc (1)
where
V: Blood velocity PA0 .theta.: Angle between an ultrasonic beam and blood stream PA0 C: sonic velocity
Arranging the formula (1) for the blood velocity V, we have EQU V=Cfd/(2fc cos .theta.) (2)
The formula (2) teaches that a blood velocity may be obtained by measuring the Doppler shift frequency "fd".
An exemplary display of the combination of blood stream information and a tomogram as obtained by a prior ultrasonic Doppler diagnosis apparatus based on the above principles, is shown in FIG. 1. As shown, blood stream information D as collected by the ultrasonic Doppler method and a sector tomogram B as obtained by the ultrasonic wave reflecting method are concurrently displayed on a monitor. In the display of the blood stream information D, the ordinate represents velocity of a blood stream, and the abscissa represents time. The tomogram B contains a blood stream S, a raster L as an ultrasonic beam, which intersects the blood stream S in an appropriate direction, a sample volume SV (range gate mark) located at the intersection of the blood stream S and the raster L, and an angle mark R rotatable about a central point C of the sample volume SV. The angle mark R may be rotated about the central point C by a desired angle .theta. by turning a rotary encoder installed on a console of the diagnosis apparatus. To set the angle .theta. of the angle mark R, an operator approximately estimates the direction of the blood stream S, and turns the angle mark so that it coincides with the estimated direction. The diagnosis apparatus is provided with such a function that when the rotary encoder is manually turned, the angle mark R turns in synchronism with the turn of the encoder, and the angle .theta. of the angle mark R is automatically calculated. Additionally, the apparatus substitutes a figure of the angle as calculated for the .theta. in the formula (2), calculates the formula to obtain a velocity of a blood stream, and finally displays the velocity of the blood stream.
As described above, in the ultrasonic Doppler diagnosis apparatus, to set the angle .theta., an operator carefully observes a tomogram on the monitor, and manually turns the angle mark R so as to coincide with the direction of a blood stream. Accordingly, the operations to set the angle .theta. are intricate. The plane of the layer of a body for obtaining a Doppler shift signal is not always coincident with that for obtaining a B mode. Accordingly, in the resultant image, run of a blood vessel and the wall of a vessel are not exact. The estimation of the direction of a blood stream on the basis of such an image possibility contains an error. Further, since the direction of a blood stream is manually set, there is a limit in improving an accuracy of detecting information on the blood stream.
The ultrasonic Doppler diagnosis apparatus as mentioned above is described in Japanese Patent Disclosure (No. 61-22576) and U.S. Pat. No. 4,416,286.